Bcl-2 and Bax in congenital naevi.

Background: Melanocytes represent a static component of the epidermis, and the role of apoptosis in basal melanocyte function and melanocytic tumour formation has not been fully elucidated.

Objectives: The aim of this study was to investigate the expression of Bcl-2 anti-apoptotic and Bax apoptotic proteins in congenital naevi in correlation with p-27 protein and Ki-67 proliferative index.

Methods: Our material comprised 30 congenital naevi (eight giant) excised from children aged from 15 days to 14 years old. The immunohistochemical streptavidin-biotin method was performed on paraffin sections for the detection of Bcl-2 (cl100/D5), Bax (cl2D2) , Ki-67 (MIB-1) and p-27 (1B4) proteins with monoclonal antibodies.

Results: Bcl-2 protein was detected in all cases showing a strong diffuse cytoplasmic expression in >70% of the naevocytes and was preserved in the deeper parts of the naevi. On the other hand, Bax was detected in 13 of the cases, showing a fainter cytoplasmic expression in 40-50% of the naevocytes without any particular topographic distribution. Ki-67 was detected in all cases showing a limited expression in 1-2% of the nuclei mainly in the junctional and upper dermal components. p-27 protein showed a broad diffuse nuclear expression (>70% of the nuclei) in all cases with a particular increase in the deeper parts of the naevi. Bcl-2 expression showed a parallel correlation with p-27 protein.

Conclusions: Broad Bcl-2 expression in congenital naevi suggests that suppression of apoptosis may play an important role in the maintenance of naevocytes despite the low proliferative activity.